• Asian Journal of Atmospheric Environment
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• 제5권2호
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• pp.105-112
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• 2011

In order to investigate the effects of local and synoptic meteorological conditions on urban scale particulate air pollutants observed over the Busan coastal area, power spectrum analysis was applied to observed particulate matter with an aerodynamic diameter $\leq10\;{\mu}m$ ($PM_{10}$) for the period from 1 October, 1993 to 31 December, 2004. Fast Fourier Transform (FFT) analysis was used to obtain the hourly mean observed $PM_{10}$ concentrations to identify different periodicity scales of $PM_{10}$ concentrations. The results showed that, aside from the typical and well-known periodicities such as diurnal and annual variations caused by anthropogenic influences, three other significant power spectral density peaks were identified: 7-day, 21-day and 2.25-year periodicities. Cospectrum analysis indicated that the seven-day variations were closely related to the synoptic meteorological conditions such as weak wind speed, which are relevant to the stagnant high pressure system slowly passing through the Korean Peninsula. The intra-seasonal 21-day variation was negatively correlated with wind speed but was consistently positively correlated with relative humidity, which is related to aerosol formation that can be achieved as a result of the hygroscopic characteristics of aerosols. However, the quasibiennial 2.25-year variation was correlated with the frequency of Asian dust occurrence, the periodicities of which have been recorded inter-annually over the Korean Peninsula.

• Bulletin of the Korean Chemical Society
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• 제35권4호
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• pp.1191-1194
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• 2014

Imaging Differential Optical Absorption Spectroscopy (Imaging-DOAS) has been utilized in recent years to provide slant column density (SCD) distributions of several trace gas species in the plume. The present study introduces a new method using Imaging-DOAS data to determine two-dimensional plume structure from the plume emissions of power plant in conditions of negligible aerosol effects on radiative transfer within the plume. We demonstrates for the first time that two-dimensional distributions of sulfur dioxide ($SO_2$) and nitrogen dioxide ($NO_2$) in power plant emissions can be determined simultaneously in terms of SCD distribution. The $SO_2$ SCD values generally decreased with increasing distance from the stack and with distance from the center of the plume. Meanwhile, high $NO_2$ SCD was observed at locations several hundred meters away from the first stack due to the ratio change of NO to $NO_2$ in NOx concentration, attributed to the NO oxidation by $O_3$. The results of this study show the capability of the Imaging-DOAS technique as a tool to estimate plume dimensions in power plant emissions.

• 대한원격탐사학회지
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• 제26권6호
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• pp.617-627
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• 2010

Although many researches for heat island study have been developed, there is little attempt to link the findings to actual and hypothetical scenarios of urban developments which would help to mitigate the Urban Heat Island (UHI) in cities. The aim of this paper is to analyze the UHI at urban area with different geometries, land use, and environmental factors, and emphasis on the influence of different geometric and environmental parameters on ambient air temperature. In order to evaluate these effects, the parameters of (i) Air pollution (i.e. Aerosol Optical Thickness (AOT)), (ii) Green space Normalized Difference Vegetation Index (NDVI), (iii) Anthropogenic heat (AH) (iv) Building density (BD), (v) Building height (BH), and (vi) Air temperature (Ta) were mapped. The optimum operational scales between Heat Island Intensity (HII) and above parameters were evaluated by testing the strength of the correlations for every resolution. The best compromised scale for all parameters is 275m resolution. Thus, the measurements of these parameters contributing to heat island formation over the study areas of Hong Kong were established from mathematical relationships between them and in combination at 275m resolution. The mathematical models were then tabulated to show the impact of different percentages of parameters on HII. These tables are useful to predict the probable climatic implications of future planning decisions.

• 한국재료학회지
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• 제31권10호
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• pp.546-551
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• 2021

To improve ferroelectric properties of PZT, many studies have attempted to fabricate dense PZT films. The AD process has an advantage for forming dense ceramic films at room temperature without any additional heat treatment in low vacuum. Thick films coated by AD have a higher dielectric breakdown strength due to their higher density than those coated using conventional methods. To improve the breakdown strength, glass (SiO₂-Al₂O₃-Y₂O₃, SAY) is mixed with PZT powder at various volume ratios (PZT-xSAY, x = 0, 5, 10 vol%) and coating films are produced on silicon wafers by AD method. Depending on the ratio of PZT to glass, dielectric breakdown strength and energy storage efficiency characteristics change. Mechanical impact in the AD process makes the SAY glass more viscous and fills the film densely. Compared to pure PZT film, PZT-SAY film shows an 87.5 % increase in breakdown strength and a 35.3 % increase in energy storage efficiency.

• 한국자동차공학회논문집
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• 제20권6호
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• pp.24-32
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• 2012

A large fraction of urban $PM_{10}$ concentrations is due to non-exhaust traffic emissions including road dust, tire wear particles, and brake lining particles. Although potential health and environmental impacts associated with tire wear debris have been increased, few environmentally and biologically relevant studies of actual tire wear debris have been conducted. Tire wear particles (TWP) are released from the tire tread as a result of the interaction between the tire and the pavement. Roadway particles (RP), meanwhile, are particles on roads composed of a mixture of elements from tires, pavements, fuels, brakes, and environmental dust. The main objective of present study is to identify the contribution of tires to the generation of RP and to assess the potential environmental and health impacts of this contribution. First, a mobile measurement system was constructed and used to measure the roadway particles on asphalt road according to vehicle speed. The equipment of the mobile system provides $PM_{10}$ concentrations by Dusttrak DRX and number density & size distribution measurements of fine and ultra-fine particles by a fast mobility particle sizer (FMPS) and an aerosol particle sizer (APS). When traveling on an asphalt road at constant speed, there is a clear tendency for PM10 concentration to increase slightly in accordance with an increase in the vehicle speed. It was also found that considerable brake wear particles and particles from tire/road interface were generated by rapid deceleration of the vehicle. The morphology and elements of the roadway particles were also analyzed using SEM-EDX technique.

• 대기
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• 제22권1호
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• pp.73-85
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• 2012

The collision efficiency data for collision between graupel or hail particles and cloud drops that take into account the differences of particle density are applied to the Takahashi cloud model. The original setting assumes that graupel or hail collision efficiency is the same as that of the cloud drops of the same volume. The Takahashi cloud model is run with the new collision efficiency data and the results are compared with those with the original. As an initial condition, a thermodynamic profile that can initiate strong convection is provided. Three different CCN concentration values and therefore three initial cloud drop spectra are prescribed that represent maritime (CCN concentration = 300 $cm^{-3}$), continental (1000 $cm^{-3}$) and extreme continental (5000 $cm^{-3}$) air masses to examine the aerosol effects on cloud and precipitation development. Increase of CCN concentration causes cloud drop sizes to decrease and cloud drop concentrations to increase. However, the concentration of ice particles decreases with the increase of CCN concentration because small drops are difficult to freeze. These general trends are well captured by both model runs (one with the new collision efficiency data and the other with the original) but there are significant differences: with the new data, the development of cloud and raindrop formation are delayed by (1) decrease of ice collision efficiency, (2) decrease of latent heat from riming process and (3) decrease of ice crystals generated by ice multiplication. These results indicate that the model run with the original collision efficiency data overestimates precipitation rates.

• 한국대기환경학회지
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• 제28권2호
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• pp.131-141
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• 2012

A large fraction of urban $PM_{10}$ concentrations is due to non-exhaust traffic emissions including road dust, tire wear particles, and brake lining particles. Although potential health and environmental impacts associated with tire wear debris have increased, few environmentally and biologically relevant studies of actual tire wear debris have been conducted. Tire wear particles (TWP) are released from the tire tread as a result of the interaction between the tire and the pavement. Roadway particles (RP), meanwhile, are particles on roads composed of a mixture of elements from tires, pavements, fuels, brakes, and environmental dust. The main objective of present study is to identify the contribution of tires to the generation of RP and to assess the potential environmental and health impacts of this contribution. First, a mobile measurement system was constructed and used to measure the RP on asphalt roads according to vehicle speed. The equipment of the mobile system provides $PM_{10}$ concentrations by Dusttrak DRX and number density & size distribution measurements of fine and ultra-fine particles by a fast mobility particle sizer (FMPS) and an aerosol particle sizer (APS). When traveling on an asphalt road at constant speed, there is a clear tendency for $PM_{10}$ concentration to increase slightly in accordance with an increase in the vehicle speed. It was also found that considerable brake wear particles and particles from tire/road interface were generated by rapid deceleration of the vehicle. As a result, the $PM_{10}$ concentration and particle number of ultra-fine particles were measured to be very high.

• 한국산업보건학회지
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• 제27권2호
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• pp.115-122
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• 2017

Objectives: This study was designed to evaluate the changes in the particle filtration efficiencies of five cloth masks (4 plate types, 1 cup type) with an increasing number of machine washings and the degree of cloth expansion. Methods: NaCl aerosols were generated using an atomizer and passed through cloth masks in a dynamic aerosol chamber. Particle concentrations were measured both before and after for the cloth masks using an optical particle counter (OPC) in the size range of $0.3{\sim}10{\mu}m$. Results: In the original condition, the filtration efficiencies of the five cloth masks were A: 20.1%, B:30.9%, C: 25.0%, D: 26.5%, and E: 40.9%. As the number of washings increased in the order of one, two, and four times, the filtration efficiencies of cloth mask C increased. The filtration efficiency of A, D, and E increased after the first washing. With the exception of B, the filtration efficiency of cloth masks increased after the second washing and those of all cloth masks increased after the fourth washing. This might be caused by the fibers untangling from the yarn and being freed at one end. In this status, the packing density of the textile will not change, but the distances between fibers will increase, which might bring about an increase in filtration efficiency. When the cloth masks were extended by 10% and 20% in one direction, the filtration efficiencies of cloth masks B, D, and E decreased at 10% extension, and those of all cloth masks decreased at 20% extension. When the cloth masks were expanded by 10% and 20% in two directions, the filtration efficiencies of all cloth masks decreased by at least 34.7% at 10% extension, and by at least 60.9% at 20% extension Conclusions: The filtration efficiency of cloth masks could decrease after one to two machine washings, but will increase after four washings in comparison with their original performances. The filtration efficiency of cloth masks will decrease when they are expanded, such as when stretching over the nose during wearing status.

• The Journal of Advanced Prosthodontics
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• 제6권2호
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• pp.96-102
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• 2014

PURPOSE. This study was performed to characterize the effects of zirconia coated with calcium phosphate and hydroxyapatite compared to smooth zirconia after bone marrow-derived osteoblast culture. MATERIALS AND METHODS. Bone marrow-derived osteoblasts were cultured on (1) smooth zirconia, (2) zirconia coated with calcium phosphate (CaP), and (3) zirconia coated with hydroxyapatite (HA). The tetrazolium-based colorimetric assay (MTT test) was used for cell proliferation evaluation. Scanning electron microscopy (SEM) and alkaline phosphatase (ALP) activity was measured to evaluate the cellular morphology and differentiation rate. X-ray photoelectron spectroscopy (XPS) was employed for the analysis of surface chemistry. The genetic expression of the osteoblasts and dissolution behavior of the coatings were observed. Assessment of the significance level of the differences between the groups was done with analysis of variance (ANOVA). RESULTS. From the MTT assay, no significant difference between smooth and surface coated zirconia was found (P>.05). From the SEM image, cells on all three groups of discs were sporadically triangular or spread out in shape with formation of filopodia. From the ALP activity assay, the optical density of osteoblasts on smooth zirconia discs was higher than that on surface treated zirconia discs (P>.05). Most of the genes related to cell adhesion showed similar expression level between smooth and surface treated zirconia. The dissolution rate was higher with CaP than HA coating. CONCLUSION. The attachment and growth behavior of bone-marrow-derived osteoblasts cultured on smooth surface coated zirconia showed comparable results. However, the HA coating showed more time-dependent stability compared to the CaP coating.

• Asian Journal of Atmospheric Environment
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• 제12권1호
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• pp.59-66
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• 2018

This study aims to evaluate the performance of the Air Quality Model (AQM) for the seasonal and spatial distribution of the $NH_3$ concentration in the atmosphere. To obtain observational data for the model validation, observations based on biweekly sampling have been conducted using passive samplers since April 2015 at multiple monitoring sites in the Tokyo metropolitan area. AQM, built based on WRF/CMAQ, was applied to predict the $NH_3$ concentration observed from April 2015 to March 2016. The simulation domain includes the Kanto region, which is the most densely populated area in Japan. Because the area also contains large amount of livestock, especially in its northern part, the density of the $NH_3$ emissions derived from human activities and agriculture there are estimated to be the highest in Japan. In the model validation, the model overestimated the observed $NH_3$ concentration in the summer season and underestimated it in the winter season. In particular, the overestimation in the summer was remarkable at a rural site (Komae) in Tokyo. It was found that the overestimation at Komae was caused by the transportation of $NH_3$ emitted in the northern part of the Kanto region during the night. It is suggested that the emission input used in this study overestimated the $NH_3$ emission from human sources around the Tokyo suburbs and agricultural sources in the northern part of the Kanto region in the summer season. In addition, the current emission inventories might overestimate the difference of the agricultural $NH_3$ emissions among seasons. Because the overestimation of $NH_3$ in the summer causes an overestimation of $NO_3{^-}$ in $PM_{2.5}$ in the AQM simulation, further investigation is necessary for the seasonal variation in the $NH_3$ emissions.